Hi I am new to the list, I see these posts are way old, but wanted to reply.
I have three Yorkies, One was a rescue that I adopted at 7 1/2 yrs old. Aftraid of his own shadow, didn't know how to play. First time I threw him a ball HE and the ball hit the wall at the same time. NOW, it's his favorite toy, "tells" me when it's time to play.
A second yorkie was a re-homed one, we removed from a sister-in-law. That one yorkie just won't play with any toys. Sure, he'll grab one and then drop it off somewhere. Will catch a ball in his mouth, sometimes, then drop it. Seems he just wants to rest or bathe in the sunlight all the time. BUT, I did find out what he REALLY likes , so I make this suggestion: TRY BEHAVIOR TRAINING/AGILITY! This one yorkie, is great at obeying commands and doing all the manuvers as required. He even bypassed the tempation to play with other dogs in the class. He just recently turned 4yrs old. So toys may not be the thing with some dogs, but, things that stimulate his/her brain is, something that isn't repetitive, but, challenging. I hope this helps.
Petlove